1. Field of the Invention
The present invention relates generally to a microwave detector for detecting microwaves transmitted from measuring equipment. More specifically, the invention relates to a wideband microwave detector which covers a wide frequency range with a single reception circuit.
2. Description of the Related Art
Multi-band microwave detectors, such as so-called radar detectors which are adapted to detect microwaves transmitted from radar type speed measurement equipment, have been known in the prior art. For example, U.S. Pat. No. 5,268,689 issued on Dec. 7, 1993 to Ono and Hatasa who are also the inventors of the present invention, U.S. Pat. No. 4,313,216, issued on Jan. 26, 1982 to Jaeger et al., U.S. Pat. No. 4,622,553, issued on Nov. 11, 1986 to Baba et al., U.S. Pat. No. 4,630,054, issued on Dec. 16, 1986 to Martinson, and U.S. Pat. No. 4,954,828, issued on Sep. 4, 1990 to Orr disclose radar detectors of the type that the present invention is directed. Typical traffic monitoring radar type speed measuring equipment (hereinafter referred to as "radar") employ microwaves in a plurality of frequency bands, i.e. 10 GHz band (X band), 24 GHz band (K band) and 35 GHz band (Ka band). The known radar detectors receive the microwaves transmitted from the radar through a heterodyne type receiver circuit, such as a super-heterodyne receiver circuit or so forth. For widening the receiving band range, a local oscillation frequency is swept.
In the microwave detector adapted to detect the traffic monitoring radar type speed measuring equipment, a target band range of detection in the X band is approximately 100 MHz and a target band range of the K band is approximately 200 MHz. Therefore, concerning the detection of X and K bands, the required bandwidth is relatively narrow. However, in the case of the Ka band, the target band range is 33.400 to 36.000 GHz (band width: 2.6 GHz), and thus is quite wide.
In the super-heterodyne receiver circuit, there are known microwave detectors capable of detecting X, K and Ka bands simultaneously by positively using not only a base frequency of the output of a first local oscillator but second and third high harmonics. However, in such known microwave detectors, only a part of the bandwidth, i.e. 2.6 GHz, of the Ka band can be covered.
In principle, it should be possible to cover the target band range for the detection of Ka band, i.e. 2.6 GHz, by providing a wider frequency sweeping width of the local oscillator. However, in such a case, the sweeping width which is required to fully cover the 2.6 GHz of the Ka band range, becomes approximately nine times of the target band width of the X band and K band. This means that an unnecessary band is swept, thereby spending an unnecessary period of time. Accordingly, the possibility of failure of detection of the target microwave in the X band and the K band is significantly increased.